During our eventful trip to Grizedale yesterday, I was chatting to the mechanic at the bike shop at the visitor's centre as he bled the rear brake of my wife's Giant NRS. He noticed the Burley towing bracket and warned me about the risks of towing with a full suspension bike. He mentioned that is increases the risk of pivot problems and puts lateral forces on the shock which can lead to failure.
As he maintains a fleet of hire bikes including multiple pivot full suspension bikes, and provide Burley trailers- I'm guessing he's got first hand experience and is giving sound advice.
I'm not too worried about my wife's bike. It very rarely tows. If it does, it tends to be on smooth forestry road downhills (like at Grizedale, when I do a cheeky section of the NFT then meet back up.) With my armchair engineer hat on, I was wondering which would put more strain on a full suspension bike; heavy off road use or towing. I'd have thought towing puts more of a contant pressure on pivots, where as heavy landings are 'spikes' of high load. I'm guessing that bushes and bearings can be loaded in tension or compression (as tension on one side is the same as pressure from the other) and from any direction. I'd have also thought that unless you develop play in the pivots, the linkages themselves prevent any lateral forces on the shock.
I'd be interested he hear other's opinions or experiences.
(By the way, hats off to the mechanic (sorry, didn't catch his name) for finding the time on a busy bank holiday weekent to do some emergency work on Mrs M's bike to salvage our day!)
This is my old ellsworth moment which i used for towing our trailer a lot last year, no effect on the pivots what so ever imo, miss that bike loads.
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I can see that
I use a BOB type trailer and if you tend to move the bike from side to side when riding as I do I can feel the trailer sort of twisting the back end of my HT (end result my backwheel fell apart because I did not tension the spokes enough yep nobber 😳 )
on the full sus it would put pressure on the pivots in the wrong direction to what the suspension is designed for as in up and down motion not side to side
saladdodger - Member
I can see thatI use a BOB type trailer and if you tend to move the bike from side to side when riding as I do I can feel the trailer sort of twisting the back end of my HT
Surely, even if you're moving from side to side, the trailer won't be putting any significant lateral force on the rear triangle. Unless the trailer is swinging from side to side (as in tyres skidding from side to side) which is virtually impossible, the trailer only provides drag on the rear axle, which is acting in the longtitudinal direction of the bike. A much bigger lateral force on the pivots would be the lateral force from the bottom bracket as you pedal, with the grip of the rear tyre preventing the wheel moving sideways.
I suppose this could put more lateral force on the pivots, but it's exerted by hard pedalling rather than the trailer.
do not knowthe theories but in real world including several 2,000ft climbs and descents no problems at all
Perhaps I should also admit to having the trailer OVERLOADED 🙄 with logs which would not help much
I was worried about this before a US off road tour with a Flux and a BOB trailer. I posted a Q on mtbr and David Turner himself said that there shouldnt be any increased wear. Either way the rear bearings are the easiest / cheapest to replace.
[arm chair engineer mode]
Although an issue with all frames, I'd guess its probably much more of issue with straight single pivot designs wear the shock attaches directly to the swingarm. If the swingarm is in torsion/flexing/whatever from trailer side loads the swing arm pivot and shock pivot are having to resist this?
An Orange 5 or Santa Cruz heckler may not be too bad given they have pretty big swingarm pivots and beefy swingarms so they themselves may reduce the flex quite well unlike some other single pivots
Linkages may help to reduce the flex on the shock but ultimately theres surely going to be some side loading on the shock due to side load on the rear triangle?
[/arm chair engineer mode]