Different sized wheels and tyres?

[bissona]

Evening all,

Was wondering if anyone was running a 27.5" / 2.6 on the back and a 29" / 2.4 on the front?

Not sure I want to increase the rake any more (the JAM is pretty laid back as it is) but prefer the idea of great edge control from the thinner tyre while leaving the back end looser thanks to the wider profile. May be a chance of counteracting the geometry change by increasing the rake using reduced fork offset?

Also like the idea of a larger rolling radius up front to cope with bigger obstacles.

Was thinking Nobby Nick on the back and Magic Mary up front, but also like the look of their new Eddy Current model which seems designed for these kind of shenanigans.

Cheers.

 

[steve_sordy]

What do you expect the overall diameters to be for those wheel and tyre combos? They may not be that different. Some tyres measure large and some don't. Get the combo right and you may end up with wheels that are not far off each other.

 

[bissona]

That's a good point Steve, backed up by the fact that there isn't a huge amount of additional clearance between my 27.5" x 2.8 Rekon and the bridge on the 29" fork.

My thinking comes from the motocross world (I dabbled previously) where even the smallest models have a fair sized difference between front & rear. I also find the 2.8 on the front ponderous in some of the rapid/twisty stuff.

Might be worth leaving a 2.8 on the back and trying the 2.4/29" on the front. Will report back!

 

[knut7]

Here's what I've found for tyre height

Dim. Dia Rad
29x2.4 744 372
27x2.8 725 362.5
27x2.6 716 358

So the hub is about 10mm higher off the ground when running 29x2.4 compared to 27x2.8. Head and seat angle will drop by 0,5*. Trail will increase because of the taller wheel and slacker HA. BB height will increase by 3-4mm. Trail will increase, but rake won't be affected, will it? Rake angle will be affected.

Going 27x2.6 rear puts the BB height back to where it started, and slackens HA and SA by about 0.25*. Trail will increase further.

Putting a 29" wheel up front seems to make it a Jam2 Drifter. Photo showing 29x2.4 DHR ll front and 27x2.8 Rekon rear. Haven't had the chance to ride it because of the snow, unfortunately the bike goes back to the dealer tomorrow.