Racks for full suspension

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Nettled Shin
Posts: 644
Joined: 1 Jul 2010, 10:01am
Location: Brigadoon

Racks for full suspension

Postby Nettled Shin » 13 Sep 2011, 3:12pm

I'd like to fit a rack to my rear suspension MTB, and I don't want a seat-post mounted one. I'd find it useful for shopping etc, and I'd also like to do some overnight off-road trips.
Many rack adverts state "not for rear suspension", but for the life in me, I can't see why a standard one couldn't be made to fit my rear triangle without interfering with the seat post/saddle. Has anyone else tried it and gotten away with it?

iandriver
Posts: 2181
Joined: 10 Jun 2009, 2:09pm
Location: Cambridge.

Re: Racks for full suspension

Postby iandriver » 14 Sep 2011, 3:38pm

These guys say their racks do full bouncers:

http://www.carradice.co.uk/categories/omm

Thought about a single wheeled trailer?
http://www.edinburghbicycle.com/comms/s ... er-new.htm
Supporter of the A10 corridor cycling campaign serving Royston to Cambridge http://a10corridorcycle.com. Never knew gardening secateurs were an essential part of the on bike tool kit until I took up campaigning.....

Nettled Shin
Posts: 644
Joined: 1 Jul 2010, 10:01am
Location: Brigadoon

Re: Racks for full suspension

Postby Nettled Shin » 15 Sep 2011, 12:00pm

Ouch, they are £70 for the Old Man Mountain racks. I don't need the one that attaches to a QR skewer, as I don't have a rear disc brake. The ones for eyelets, like the Red Rock, don't look unusual. I'm minded to buy a bog standard rack and make it fit. I'll learn something from the exercise.

iviehoff
Posts: 2411
Joined: 20 Jan 2009, 4:38pm

Re: Racks for full suspension

Postby iviehoff » 20 Sep 2011, 11:39am

Nettled Shin wrote:I'd like to fit a rack to my rear suspension MTB, and I don't want a seat-post mounted one. I'd find it useful for shopping etc, and I'd also like to do some overnight off-road trips.
Many rack adverts state "not for rear suspension", but for the life in me, I can't see why a standard one couldn't be made to fit my rear triangle without interfering with the seat post/saddle. Has anyone else tried it and gotten away with it?

The frame geometry of rear suspension bike frames is diverse. They will state "not for rear suspension" because many rear suspension bikes do not have a rigid rear triangle of suitable geometry to fit a standard rear rack, in fact there are some that don't even have a rear triangle. If in your case you have a rigid rear triangle of similar geometry to a hardtail bike, you might be able to fit it.

If you are going shopping for eggs, you should note that a rack fitted below the suspension, as it were, will get a lot more shaking than a rack fitted on the suspended part of the bike. However fitting to the suspended part of the bike can be tricky, as your refusal to have a seat-post rack indicates you already understand. The problem is that typically you don't have the multipoint fittings of a hard-tail bike to obtain a strong but light framework, so either the load is reduced, or it has to be reinforced.

hamster
Posts: 3202
Joined: 2 Feb 2007, 12:42pm

Re: Racks for full suspension

Postby hamster » 26 Sep 2011, 9:44am

The suspension is fouled up by 10kgs or so of stuff hanging onto the suspension arm. The damping will be inadequate and the wheel won't rise as fast due to the extra unsprung weight.
So at the end of it you get a bike with the suspension not working, so the point of suspension is taken away. It's simpler just to use a hardtail frame if you want to tour.

Nettled Shin
Posts: 644
Joined: 1 Jul 2010, 10:01am
Location: Brigadoon

Re: Racks for full suspension

Postby Nettled Shin » 26 Sep 2011, 5:18pm

hamster wrote:The suspension is fouled up by 10kgs or so of stuff hanging onto the suspension arm. The damping will be inadequate and the wheel won't rise as fast due to the extra unsprung weight.
So at the end of it you get a bike with the suspension not working, so the point of suspension is taken away. It's simpler just to use a hardtail frame if you want to tour.


It's not ideal, I know, but having two mountain bikes is problematic. You'll have to persuade me a bit more before I fully accept your answer. The wheels are forced to track the ground on the compressive side of bumps, so there could be an elephant on the rack and the wheel would still rise. In this case the suspension is still able to do its job of isolating the rider from the vertical wheel motion. The extension of the suspension might be a bit slower when the terrain is dropping away, but isn't it deliberately slowed anyway using rebound adjust on most shocks? Or how about thinking like this: aren't the spring rates for a bike's suspension normally selected based on the mass of the rider, not the mass of the wheels?

hamster
Posts: 3202
Joined: 2 Feb 2007, 12:42pm

Re: Racks for full suspension

Postby hamster » 26 Sep 2011, 7:14pm

You are correct in that the wheel would still rise. However, the rate of rising will be slower as it has to accelerate the wheel , suspension etc AND ALSO the mass of panniers. In the same way, it will continue going as it all starts swinging. As the suspension tries to track downwards it will overshoot. It's about the dynamic response not simply a static loading. Consider riding over a simple speed bump. The wheel etc has to rise rapidly. If it rises too slow, then the bike lifts. After that, it has to stop rising, as any overshoot would cause the bike to dip. This is the problem with increasing unsprung weight - you will need dramatically different spring and damper settings as the extra weight is unsuspended.

In summary your suspension won't work as intended. It's up to you if you want to ride your bike like that, and I agree that owning another bike is not necessarily ideal. For a normal bike (as you say) suspension is selected on the mass of the rider, as the wheels plus suspension is a couple of kilos and relatively trivial. But change that to 15kgs and you are dealing with 10x the weight in the moving parts.

WaitForPete
Posts: 17
Joined: 3 Oct 2011, 5:05pm

Re: Racks for full suspension

Postby WaitForPete » 3 Oct 2011, 5:47pm

Another option is a seatpost-mounted saddlebag with a hangar, though you would need to check the clearance with the suspension fully compressed.

I use this setup for off-road Enduros, though the Hei-Hei only has 2.5" of rear travel.