King of the Mountain

2008 Fuel EX Geometry

We've had a lot of questions about the geometry of the new EX. The basic geometry and handling of the 2007 EX has been carried over to this new bike. We went through a lot of iterations and testing to get that bike dialed as far as the geometry and handling was concerned, so we didn't feel a need to change what was working so well.

The effective top tube length and overall cocpit area is something we've had worked out for quite a while, going back to the original Fuel bikes. It gives you a good amount of room to stretch out and keeps your weight centered in the bike, but still allows you to very easily weight the bike forward or back depending on the terrain (trail obstacles, or big descents for instance).

The BB height was something we experimented with quite a bit. What we finally settled on was an excellent balance of keeping your weight as low as possible for stability and the ability to really rail corners, but at the same time, keeping it high enough to avoid bashing chain-rings into logs and rocks.

We really put a lot of effort into the steering geometry. Here our objective, and what we attained, was a very balanced handling - responsive handling to keep things sharp in tight, twisty trails, but stable enough to be able to really open it up on big descents.




hi, i bought a new 2012 fuel ex 7, im 5'10" , my local bike store only have the 17.5 size, used it on a trail and its okay, but i'm still thinking if i should have waited for the 18.5.

do you think 17.5 virtual size really fits me or not?


i'm 1.57 cm and i would like to buy the trek ex 7 15.5 is right for me or better no thanks


Hi, can you help me?

My measures:

height: 174cm (without shoes)
inseam 80cm (without shoes)

I want to buy a fuel ex 8 2012.

The right size was 17,5 8 18,5?


Gregory Cashmer

I'm 5'8 1/2" with a 33" inseam (based on placing a book between my legs and measuring from the floor to the top of the book. Will I fit on a 19.5 Top Fuel 9.8?

James Hutchinson

I just bought a 2010 Trek Ex5 at my local shop, Bumsteads. I am 6ft, 210lbs, and my Ex5 is the 17.5 size. It felt ok, but looks small, and when I was questioning the size, the shop asserted that this size would be fine for me. Is this size really going to work for me? I have not taken it to the mountain yet, in case I need to sell it and start over.

Dean Biker

Hi, having trouble working out what frame size I'd need. It's either 17.5 or 18.5 I think.

I'm 5ft 8 or 173cm high
Inside leg is 82cm

The site says smaller's usually better so is 17.5 the better?


I want to buy Fuel Ex 8, I am 185 cm and 83 cm height, frame size battery do you recommend me?. I love traveling, not race.

Thank you

Jake's Knee

Hi Dylan
Treated myself to a new 2010 Fuel EX recently. Was suprised to find on 17.5" size frame the crank length to be 175mm. I'm 175cm tall with an inseam of 79.5cm. I've had to crank my seat all the way forward to get good alignment of my knee with the pedal axle. My guess is a 170mm long crank would suit me better. Is 175mm the correct length that is supplied with this frame size? From my expereince it seems that bit too long.

David S

I am 5 feet 11 inches. 33 inch waist, 185 lbs. I have a Trek 4500 19.5" it felt too big. Now I found a great deal on a 17.5" FUEL 90. Should I get it???? will this feet? I have been reading a lot about mountain biking, and suppostly the smaller you can get away with is what will be best for hardcore trailing? or I am wrong?

s morris

I am looking at a 2008 trek ex9 that is a size 18.5. I am 5'9"-5'10" tall with a 30 inch inseam. Would that bike fit me or would it be too big? I do all around riding.

Angus Bloomfield

I'm just about to order a Fuel EX8 but can't decide between the 19.5" and 21.5" sizes because I can't find a 21.5" in the country to test ride! I'm 6'1.5" with a 32" inseam. Previous feedback suggests a 21.5" but I have a longish back and shortish legs. Many thanks in advance.


Hi I am 5foot 6Inches with 30 inches of inseam. I test the 15.5 size but I think its to small and i think the cranks are 170. But the 17.5/16.5 top tube seems to long(23.2) for me. At this moment I am using using a small 16.5 frame with 22.6 top tube with a 100mm steam. So what are my options.


Hi, my wife is looking at a 2009 Fuel Ex8 WSD. She is 5'9" with fairly long legs
(probably a 31" inseam). Do you think a 17.5 frame in this bike would be okay for her? Thanks.

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Hi, I am on the way to buy a Trek Fuel EX 8 WSD model 2008, I'm 1.64m tall, the vendor told me that the 18" fits to me, I was a litle bit surprise, don't you think a 16" would be better?

Hi Vaérie
I am also be surprised at the 18" recommendation. For your height, a 16" would probably be much better.


Hi, as a follow up, I took your advice and went with the 19.5 large. It is perfect! I'm 6 feet tall with a 34" inseam. I run the seatpost on the 6th hash mark down (of 11 hash marks) which leaves me just over 1.5" of post left until I hit the min. insertion mark. This puts the saddle height just about even, or slightly above the handlebars (with all 3 spacers under the stem). The reach is perfect. I run the saddle fore/aft setup with the saddle slid slight back of the center of the seat rails.I think that on an 18.5 I would have to have the post right at the max and on an XL I would be a little stretched out from seat to handlebar.
The bike is just awesome! I love it! Hope this helps anyone else out there trying to figure out which size to go with.


Hi, great responses! I'm going to buy an 09 Fuel EX 8 and am debating between a size large or XL. I'm 6ft even with a 34 inch inseam. I think the reach is good on the large but I need to run a little more seat post out of the frame than I would like. I can test ride a large but don't have access to an XL to try. My initial feeling was an XL, but then people tell me large, and so I'm totally on the fence. In a Trek road bike I ride a 60cm (can ride 58, but a little small) with a 110 stem if that helps...Any thoghts? Thanks for the help!

Hi Tony
I'm just a bit shorter than you with a 32" inseam and I'd consider myself a little on the fence on sizes too. I can ride an 18.5 or a 19.5 comfortably, but I've gone for the 19.5 as my everyday ride as I like being just a bit more stretched out on that bike, and I haven't felt the length has hindered me at all on tight single-track.
I would suggest going with the 19.5. From everyone I know, the XL works best for guys who are over 6' tall. The seat tube on the EX is a bit shorter than normal which was done to help lower standover. But with the large 31.6mm dia seat post, having a lot stick out isn't a problem so long as you aren't past the minimum insertion mark.
For another view, check the comment on the EX geometry page from "Sean." Travis Brown gives a good reply and perspective on size.
But my advice would be to go with the large, especially if the reach feels good.


Rick Koppin

Another buyer here agonizing over size. I'm 180 cm tall with a 85 cm inseam. I rode the 18.5" and the bike store guy said I had alot of stem showing. They didnt have the 19.5" in stock, so I didnt get to try it out. Based on the above it sounds like you would say 19.5" with a shorter stem. What do you think?

Reply:'re a bit of a tougher case than usual. Of course, the answer I want to give you is to ride them both and try to decide which one you feel the most comfortable on. But I know how this can be difficult sometimes.
Based on your height and inseam, I would probably say go with the 18.5. You'll have a bit more seat post exposed than average, but it will still be an okay amount. The 18.5 will give you a bit more room to play around with the cocpit lenght than the 19.5 would where you'd need probably the shortest stem possible. Basically, you'd be all the way at the end of the adjustment range, where the 18.5 will put you more in the middle of the adjustment range for the cocpit (combined top tube and stem lenght).


Ace in Thailand

just the forum I need.

71" tall (180 cm)
35" inseam ( 89 cm)
24.50" arm length (62 cm)
58.50" Sternum notch (149 cm)

!7.5 or 18.5?? 2008 Fuel EX 9+

Thanks from Chiang Mai Thailand

Hi Ace
Given your height and inseam, I'd go with the 18.5. The 17.5 will have way too much seat post sticking out. You'll also be a bit more comfortably stretched on the 18.5.


Victor Schepisi

Are the psi shock settings any different being the 08 EX has a XV shock?

Editor's note: 2009 Fuel EX suspension settings can be found here:

Chip Crowther

I am planning on getting the fuel ex9.9 and Top Fuel 9.8.
I am 6' with a 83cm inseam.
Which size would you recommend 18.5 or 19.5?

Hi Chip
At your height, you could really go either way and be comfortable. The biggest thing depends a bit on your riding style and terrain. I'm just a bit under 6 foot myself, and I ride the 19.5. Although I do prefer to run a shorter stem than stock (80mm reach). I like the extra stability the slightly longer wheel base gives, but I still don't feel that the longer wheel base hampers tight single-track maneuverability at all.
For overall riding, in most terrain, I'd recommend the 19.5 for your height.


Anibal Alejandro Diaz-Campos

I weigh five feet seven inches (5 '7 "), and in the shop recommended a Fuel EX 8 2008, Size 17.5 virtual current 16.5.

My question comes in the wake of several fellow mountain bikers tells me that my ideal size is 15.5.

What really is the size recommended for me?

I run different styles for fun but sometimes competes.

Thanks for the help you can give me.

Hi there
Based on your height, I would still say you should go with the 17.5 (16.5 virtual). Our bikes are designed with slightly longer top tube lengths than average. However, they are also meant to be used with slightly shorter stems than average. If the stock set-up still seems long, try one size shorter stem. But based on your height, and some other guys here who are your size, I would agree with the shop and go with the size 17.5.


Phil Howieson

No need to post this, just writing to thank you for your response. I'm buying the 19.5" and putting on a shorter stem (and cutting down those ultra-wide bars)to sharpen up the feel.

The fact that the senior R&D engineer replies to this sort of mundane stuff is just one of the reasons I'll be buying another Trek. If you guys are looking to hire another industrial designer let me know and I'll send you a copy of my portfolio.




Hi greetings from belgium

im 176cm with inseam of 86 cm
my local dealer said a 19.5 frame would be fine . i tried a 19.5 and felt to long , even a 18.5 didnt feel right. althoug i could not try a 17.5 thats the one i ordered . my previous bike had horizontal tube lenght of 59cm wat fits fine , my older cannondale has 60 cm and even with shorter stem feels to stretcht out. So still im a little confused i did the right thing
greeting peter

Hi Peter

It seems to me you’ve got a pretty tall inseam for you height, which is why I can see how the larger frames feel too stretched out for you.
There’s no strength issue with riding a smaller sized frame. You might need to get a longer seat post than what comes stock with the bike. The frame is plenty strong enough to with stand using a longer post – however, you must be sure that the post is not sticking out past the minimum insertion point. And even then, a good check is to measure and make sure the bottom of the post is below the bottom side of where the top tube connects to the seat tube.
Otherwise, there is no issue riding a smaller size frame so long as you are comfortable on it and it suits your normal riding terrain and your riding style.
Enjoy the new bike!


I am looking to order an EX8, my LBS has a 19.5 sized frame in which they said is my size. I am 186cm 82cm inseam. You seem to suggest that I should get a 21.5 frame. I do a lot of steep climbing and descending which I suppose the long frame is best for, apart from the extra weight, but I also do a lot of tight single track in races and my local trails, so a shorter wheelbase is good for that, and less weight. My current hardtail has a 1090mm wheelbase. Which is the best option to get the do it all bike?

Hi Jay
We make size recommendations based on averages. However, no one is really average. What you have to consider as well is your normal riding terrain and your riding style. If you feel more comfortable on one size compared to another, always go with the one you feel more comfortable on.
You’re just a little bit taller than I am (181cm tall, 81cm inseam), and I ride a 19.5 size EX. I’ve ridden both the 18.5 and the 19.5 size pretty extensively, and I still keep coming back to the 19.5 as my favorite. My normal rides include a lot of pretty tight singletrack, and I’ve never found the bike’s wheel base to be too long. I ride pretty aggressively and I also use a much shorter stem than stock (80mm) to get the position I want. To me, my bike fits and rides perfectly.
That said, based on how you said you ride most of the time, you’ll be fine with the 19.5 size as the best “do it all” bike.
Hope you enjoy your new EX


My local dealer measured me when I was there to order a Fuel EX 8.
He told me that I in theory would need an 18,92" frame.

Now my question is:
What would be the difference between the 18,5" and the 19,5"?
On what size will I have the most upright (comfort, all-mountain) position and on which will I have the most "lying" (race, cross-country) position?

Hi Jordan
You'll be more upright on the shorter 18.5 size, and more stretched out, "race" position on the 19.5. However, don't forget to take head tube length into account when sizing like this, and how many spacers you would need.
However, for all around riding, I would suggest the 18.5. This will be closest to what your dealer theoretically measured you at, and it will also be easier to make into a "race position" type bike with a longer stem if that's what you wanted.

Phil Howieson

Hi, I'm looking into buying a Fuel EX8 after demoing one at the world cup in Stromlo on the weekend. The suspension felt perfect - plush like a coil spring but not wallowy. I normally ride the more diffuclt stromlo trails very aggresively, dabbing my foot on hairpins and snapping down out of berms, etc.

Currently my favourite (and fastest) bike to ride is my old Trek VRX. The weird thing is that I'm 6ft with an 83cm inseam and the VRX is a 16in frame. I know this is too small, but it actually feels right with the seatpost at it's highest - my leg is almost straight at the bottom of the stroke too. The 20in norco fluid I've been using for the last few months feels slow and dim witted in comparison - it feels less nimble, vauge, and i cant weight up the front as well on tight hairpins. Other bikes i've ridden (including the 19.5in fuel) had simmilar feelings. I also felt more encouraged to just sit on the saddle instead of moving around the bike.

Now I know I should be looking at at least a 19.5in frame when I buy the Fuel, but I want to know what's wrong with a frame that's too small? If I can get a seat to the right height is there still a problem? I know that the steerer angle is slacker on the Fuel, but I think a smaller frame would give me the "chuckabillity" I'm after? I know I could just work to change my riding style, but it's a question that's niggling at me.

sorry for the essay and thanks in advance for your reply,


Hi Phil,

There’s not really too much wrong with riding a bike that’s a size small as long as you can get everything in the right place – seat height, bar height, etc.

The biggest concern I would have is getting your seat to the right height. If you can get there with the stock seat post, no problem. If you have to use something abnormally long, I’d get a bit concerned about the extra leverage that would put on the frame. But if you can get there with the stock post, or something in the 400mm range, you should be just fine.

I’d recommend the 18.5 size for you at your height, but if the 17.5 really works for you, go for it.

But again, given your description of how you ride and what you’re looking for (which is how a lot of us here ride!), I would say go with the 18.5 size frame, but also change out the stem to something like an 80mm reach stem. The short stem is one of the biggest factors in increasing the “chuckability” of the bike.

Thanks for the comments, hope you enjoy the bike!



I am 178cm tall. I ride Trek 8000 19.5" which feels too stretched even with -2cm stem. I have tested Fuel EX 8 in both 18.5" and 17.5" sizes and tend to prefere 17.5" (... virtual / actual 16.5"). Is this size still acceptable given my hight? Thank you very much in advance!

Hi Michal
At your height, you should still be fine on the 17.5. It's very important to take your normal riding terrain and riding style into account when sizing your bike. So long as the seat post isn't out past the minimum insertion point, you'll be fine on the 17.5 if that's what feels better to you. Hope you enjoy the new bike


I just bought the 21.5" 2008 EX8 and I am 6'-2" with a 34.5" inseam. I feel like I made a mistake going with this size. My LBS said I was a 21.5" without a doubt. I rode the 19.5" and the cockpit did seem a little tight, but the cockpit on the 21.5" feels almost too long. I noticed that the stem length on the 19.5" and 18.5" is 100mm while the stem length on the 21.5" is 120mm. I have already moved down to a 110mm stem, but my elbows are still locked out. I always assumed that you needed a slight bend in your arms. Also, with the 110mm stem the front axle is still behind the handle bars by about 0.75". I am wondering if I should have gone with a 19.5" with a 120mm stem. I noticed that you run a 80mm stem so I wont feel too bad about moving down to a 100mm stem. What are your thoughts??


Hi Sean,

I’d recommend going with a 100 or 90 stem. That should move the bars back just about the right amount from what you describe in your email. I’m a big fan of shorter stems.

At your height, you probably could have gone either way. But I still think you made the right choice with the x-large. Our geometry is designed to be run with a shorter stem and works well that way.

For another perspective, I forwarded your email on to Travis Brown to get his opinion as he’s about the same height, and rides and XL.

I am 6' 1 1/2" and I ride a 21.5 in an EX with a 100 mm stem. I can ride a 19.5 but I prefer using a Joplin post when I am on the L. For a fixed saddle height the longer wheel base of the 21.5 is better and it looks like we are close to the same height. I would suggest a bit shorter stem is the best fit solution rather than the smaller frame.

Travis Brown”

Hope that helps a bit and you enjoy your new EX.
- Dylan


I have been reading through the sizing comments above. I am 6'2" and I am riding on the 18.5" size of the 08 Fuel EX 8 and I think it is fine... is there something that I am missing? I can't immagine having all of that extra bike and weight below me if i went with your reccomended 21.5" size.

There's nothing wrong with riding a smaller size frame if it works for you. We make size recommendations based on averages - but no one is really average. Taking riding style and terrain into account when sizing a bike is very important to getting the bike to work properly for a given rider. So long as your seat post isn't past the minimum insertion mark, it's fine to ride a smaller size frame if that's what you're comfortable on and it works for you.


I'm looking at upgrading to the Trek Ex8 WSD however as I am only 4ft 11" am wondering if the 71.5 degree seat angle would mean that the 530mm top tube would feel longer on my current bike where the top tube is the same but the seat angle is 73.5 degrees. I currently have a short stem and have been told I wouldn't want a longer overall reach. Unfortunately here is New Zealand I would have to commit to the purchase before the bike would even be brought into the shop for me so a test ride is out of the question

Hi Janine. If your current bike has the same top tube length, but a steeper seat tube angle (73 vs 71.5 on the EX), your reach to the bars will actually be slightly shorter on the Fuel EX. The measurement I'm referring to here is what we call reach - reach is the horizontal distance from the center of the top of the head tube to a vertical line from the center of the bottom bracket.
So with the same measurement for top tube, with the slacker 71.5 degree seat tube angle, you pull the Reach measurement back.
Bottom line, the EX 8 would still fit you as well or better than your current bike.

Hope this helps,

Dylan Howes



I'm in a little different boat. I am about to purchase an EX 8 and I rode the 18.5 which felt pretty good. I am 5'9" with long 32" inseam for my hight. I was curious if I should go down to a 17.5 or stay at the 18.5? Thanks! Amazing bike!


I've just test rode an EX9 and there is no doubt that this is the bike for me! Sorry for yet another frame size question but I am a little confused - I'm 5'11 tall also, and I rode the 18.5 bike. It felt comfortable but it had a lot of seatpost exposed. When I looked closely at the post markings i was only one third of the way towards the maximum mark... so in theory there is still quite a bit to go. My question is, should I stick with this frame size? i ride mostly tight fast single track.


I typically fit my bike not by seatpost exposed, but by how comfortable I am in the cockpit. I would give the 19.5" a try and see how it compares to the 18.5."

-Michael B., Trek MTB Brand Manager

Dendrinos Vassilis (vassilis)

I've already a hardtail Trek 8500 (model 2003) size Large (19.5)
I am 1.82 (6ft) with 85cm inseam and 60cm arm lenght.
I find the 62.5cm (horizontal top tube) to long for me
and I setup the bike with 9cm stem and rise handlebar.

Now I'd like to buy the Fuel EX9 but I can't decide about the correct frame size between 18.5 and 19.5.
The 18.5 has definitely the correct top tube (61cm-24in) for me but to short seat tube (44.5cm-17.5in).
So I extent the seat tube to the upper limit. The level of the saddle is above of the level of the stem
about 5cm
On the other hand the Large frame has the correct seat tube but to long top tube (62.8cm-24.7in) for trail bike, so I suppose I can't manage the bike in technical terain. I believe according to my previous experience this is no choice for me.

I've read very careffuly your comments about size.

What do you advise me about the correct frame size?

If it is possible do not post my question to your site but send your answer directly to my mail account.


I understand what you say about the long top tube, however I'm pretty close to your height - 5 foot 11 inches, with a 32 inch inseam (81cm). I find the 19.5 size frame to be a very good fit for me, even in very tight technical terrain. I currently run my bike with an 8cm stem, but I very much like shorter stems on all my bikes.

Something to keep in mind is that the Fuel EX has a less steep seat tube angle than the hardtail, yet it still has the same top tube measurement. This means that the "Reach" measurement is actually shorter on the Fuel EX than on the hardtail.

Reach is the measurement horizontaly from the center of the head tube to a vertical line through the BB. By having the same top tube measurement, but a less steep seat tube angle, you effectively pull the head tube a little closer.

I think for your height, the 18.5 will be too short vertically and you will have too much seat tube sticking out, and the handlebars will be too low.

Try to take a test ride on one at your local dealer.



Like everyone else Im struggling as to what size EX-9 for me. Im 5' 11" with a 32 " in seam but felt not too bad on a 18.5" framr. According to your above responce, would I really benefit going up to a 19.5" frame? Thanks

I'm exactly your height and inseam and I really like the 19.5. I've gone back and forth a bit on the sizes, and I can very comfortably fit both. I really like the extra bit of coqpit room on the 19.5 and the extra bit of stability you get from the slightly longer wheelbase.

I will say that I ride a shorter than stock stem - an 80mm stem with just one 5mm spacer under it.

I'd say it would depend on the terrain and your riding style. For all-around use, I prefer the 19.5 size. But if I were riding mostly very technical terrain, I could see some benefit to going with the shorter 18.5 size as this would put you in a slightly more upright position.



I am 6 ft. and ride a 20 in. Giant Trance . I have a EX8 19.5 ordered , is this on target . Thanks

you will have more seatpost extension on the EX compared to the Trance. However, based on their sizing and your height, the 19.5 should be right on target for you.


Hi, I'm torn between a 17.5 and 18.5. I measure 174.5 cm and my inseam is 83.5. Would the longer wheelbase of the 18.5 help keep the front end down on steep technical climbs?

"I'd really try to test both if you can. For your height, I'd be inclined to recommend the 17.5, but your long inseam would give you quite a bit of seat post extension. The longer wheelbase would help you keep the front wheel down as you say, I'd just be concerned you might be stretched a bit.
If the seat post extension on the 17.5 was too much, then I'd recomment the 18.5, but swap out the stem for a shorter one.


Im only 5' 7". i went with a 18.5 EX9. When I sat on the 17.5, the cockpit felt too scrunched. Im sure the standover height would have been more ideal with the 17.5. Is the actual standover height greatly reduced when I lock the front forks out at 90mm?

"The standover would be reduced by about 15mm using the 90mm setting on the forks. However, this really isn't an ideal solution to standover height. Lowering the forks also lowers the BB that same 15mm, and increases the headtube angle by about 2 degrees. This is great for getting the front end of the bike down for long, extended climbs. But for all around riding, it's really not how the bike was designed to be ridden. Hopefully your standover, even if not ideal, is still enough.
Enjoy the new ride!


Hi, I have a big concern about what size should I buy (the new 2008 EX)... I'm 1.89m and an inside leg of 87cm... Should I go for a 18.5" or a 19.5"??


Reply - At your height, I would highly suggest trying a 21.5" size frame. I'm 1.80m tall with and inside leg of 82cm and I fit a 19.5 very well. Most everyone I know who is over 1.83m tall, including Travis Brown, rides a 21.5" size frame. if you can test ride one before hand, that is always the best. But at your height, I would again highly recommend you go with the XL (21.5") size.
- Dylan Howes


Going by top tube length I would be on a 17.5 which measures 16.5 from the crank bolt to the top of the seat tube. That's a lot of seat post exposed, is that what Trek recommends? Or would one go with a longer top tube and compensate with a shorter stem?

Answer: If you can get the correct saddle height without going past the max height limit on the seat-post, then this is what we recommend. However, keep in mind that Trek's sizing is somewhat longer than what many people consider "traditional" mountain bike sizing. Try both the 17.5 and the 18.5 sizes out with your dealer or with one of our "Ride the Best" Demos. - Dylan Howes

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