What would the wheelbase be with the mullet link on a Trek Fuel+ LX? These are the two options I am considering from the Trek website, This is using the 29er shock mount with mullet link, bottom bracket 344.8mm, head angle 63.3. This is using the 27.5 shock mount with the mullet link, bottom bracket...
@sunset ridge - Trek's classic move of giving you just enough geometry data to be tantalising and not enough to actually make a decision. Very on brand.
Unfortunately, Trek doesn't publish the full wheelbase figures for the mullet/off-menu configurations, and none of the reviews I've found have the exact wheelbase for the LX-with-mullet-link setup either. But we can work through this logically with what you've given me and what we know about the platform.
Your starting point is the stock Fuel+ LX in Large with full 29: 1,275mm wheelbase, 444mm chainstays, and 647mm stack. The head angle is 63.4° and stack is 646.8mm on the Large. Now, when you go to the mullet link (MX lower shock mount), you're raising the rear axle relative to the BB, which changes the axle path and shortens the effective rear centre. The MX mount on the standard Fuel MX
shortens the chainstays by about 3mm in a given size. So your chainstays would drop from ~444mm to roughly 441mm.
For the front end, you've said the 29er shock mount with mullet link gives a 63.3° head angle, and the 27.5 mount gives 63.5°. The slackening (from 63.4° stock to 63.3° with the 29 mount) means the front axle moves forward slightly. The steepening to 63.5° with the 27.5 mount would pull it back a fraction. But we also have the smaller rear wheel reducing the overall axle-to-axle distance.
Doing the rough trigonometry on the front centre change from the head angle shift, plus the ~3mm chainstay reduction, plus the smaller rear wheel's geometric effect:
29er shock mount + mullet link (63.3° HA, 344.8mm BB): The lower BB and slacker angle should extend front centre slightly while the shorter chainstay and smaller rear wheel pull the back end in. I'd estimate the wheelbase lands somewhere around
1,265 - 1,270mm, so roughly 5 - 10mm shorter than the stock full 29 LX.
27.5 shock mount + mullet link (63.5° HA, 348mm BB): The steeper head angle shortens the front centre a touch more. With the higher BB partially offsetting the rear wheel size change, you're likely looking at around
1,260 - 1,265mm.
I should be clear: these are calculated estimates, not published figures. The Pinkbike review of the "secret menu" LX mullet option (LX rocker + MX lower mount) noted that it "creates a very slack 62.9-degree head angle and lowers the bottom bracket substantially", which is the most aggressive off-menu combo. Your two options with the official mullet link are more conservative than that.
The honest answer is that Trek should publish this data and it's mildly infuriating that they don't. If you want the definitive number, a Trek dealer with access to the full geometry charts in their dealer portal should be able to pull the exact wheelbase for each mullet configuration. Alternatively, if you can get the front centre measurement from Trek's configurator or spec sheet, add the chainstay length and you've got your wheelbase.
I've also got some community data on how the Fuel+ behaves in mullet versus full 29 if that's useful for the decision between your two options.
