jpc6000

I want to buy an new aluminium bike frame. When I find an interesting frame, mostly their are no information what the height of the suspension fork is need for the frame. Can I measures myself? They write that I can use fork 80/120 suspension. (450mm / 520mm axle to crown height) Is this true? Or only with an XC frame?

XC frame is good for fast e-bike on road?

unterhausen

If you are going to buy a mountain bike frame, then an XC frame is the one you want. A DH frame has much more relaxed geometry.

I think I would try to find an older XC frame for road ebike use.

If the manufacturer tells you 80/120mm suspension fork, I think I would believe them. But that's quite a range of forks.

Andrew R Stewart 

I have found the willingness to be "flexible" in resulting geometries in the MtB world somewhat odd. But then since the suspension forks are a constantly changing A-C dimension (during a ride) I guess this lack of concern about steering geometry (compared to the road world) kind of makes sense, if they can't nail down what the geometry is then why even bring specifics up? (That said with an amount of tongue in cheek). Andy

unterhausen

People who design mountain bikes usually look at the sagged geometry. Or at least that's my understanding. So they are thinking of a particular fork length. 80/120 A-C must not really mean what it looks like it means. 120 sags to 90, I think. Maybe someone that knows mtb geometry a little better can comment

guy153

When I made a hard-tail it seemed like everyone else was assuming 25% fork drop in their numbers. Citation needed, I can't remember where I found this.

I measured the fork fully extended at 555. It was a 140mm travel fork so I subtracted 25% of 140 from that so designed the frame on the assumption the fork was 520mm long. It worked out pretty good. The head angle at 25% drop was 65 degrees. I also estimated what it would be at full compression and can't remember the number but I think it was about 71. I wanted to know it wouldn't go outside the range of what one might consider reasonable (I guess 74 max).

I don't know what you do for full-suss. Would be fun to try and make one of those one day but need to get my head around how to design the rear geometry.

unterhausen

I have always heard 25%, that's where I got 90mm from. So whatever the un-sagged A-C is minus 30mm
That's fairly close to 80, so I'm not sure if that's not what 120/80 means.