Pannier racks for 27.5+ boost spacing MTB

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DaveE128
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Pannier racks for 27.5+ boost spacing MTB

Postby DaveE128 » 3 Jun 2019, 12:27pm

Hi,

I'm looking at buying an e-MTB for commuting (several miles of my commute are off-road and some parts are relatively rough - rideable on my gravel-type commuter with care but it's rough on the wrists) and I've seen a 27.5+ bike that seems quite suitable for my needs. I'll want to put a pannier rack on the back so I don't have to get a sweaty back. The plus tyres will hopefully reduce the amount of shock and vibration passed to my luggage a little.

The frame has eyelets at the dropouts and at the top of the seat stays.

I'm not sure what kind/size of rack I'd need for this, or whether the boost rear end or the 650b x 3" tyres make a difference. I suppose I need a "29er" rack as the tyre outside diameter is probably similar - I imagine that a 26" / 700c rack (lots of what's on the market) won't be tall enough?

Would the "boost" width of the frame cause problems with standard racks? I think it's 6mm wider than a traditional MTB - I imagine that most racks will flex to fit ok - there seems to be no standard for eyelet spacing anyway and all the racks I've fitted have needed a bit of flexing to fit. There's a bit of doubt in my mind though.

The disc brake is between the chain stay and seat stay so I don't think I need the "disc" version of any rack as these are shaped to clear a disc caliper.

I imagine the diameter of the tyres mean that the chainstays are plenty long enough for heel clearance on panniers?

Any thoughts appreciated!

slowster
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Re: Pannier racks for 27.5+ boost spacing MTB

Postby slowster » 3 Jun 2019, 1:05pm

The Boost dropout spacing will be less an issue than the 3" tyres. The inward sloping struts which provide rigidity on many rear racks, e.g. like the Tubus Cargo and Logo, will probably not accept a 3" tyre. I doubt that even the extra height of the 29" version of the Logo will compensate sufficiently for the inward sloping struts to allow a 27.5" x 3" tyre.

You can buy rear racks intended for fat bike tyres, which typically don't have inward sloping struts, but I think they are spaced for much wider dropouts than the Boost spacing. For example, Tubus' Fat rack will accept 4.8" tyres, but the spacing where it attaches to the dropouts is supposed to be in the range 205mm to 235mm. However, since the Tubus Fat rack is steel you would probably be able to cold set it to fit Boost spaced dropouts.

Tubus provide the measurements for each of their racks on their website (click on the Technical Drawing links). This is the page for the Fat rack and this is the accompanying Technical Drawing.

I suspect you might be exchanging a sweaty back for a muddy one, since there are no full mudguards generally available for 3" tyres.

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robgul
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Re: Pannier racks for 27.5+ boost spacing MTB

Postby robgul » 3 Jun 2019, 2:39pm

I'd be surprised if a bog standard rack didn't work - I've fitted loads, together with mudguards, to this electric bike in my shop - it has fat tyres and disc brakes. The rack and guards need just a slight modification with the mounting bolts to clear the callipers on the nearside. https://www.rouxbikes.co.uk/collections ... -big-slick BTW - bike is very good value at the price point

slowster
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Re: Pannier racks for 27.5+ boost spacing MTB

Postby slowster » 3 Jun 2019, 3:09pm

robgul wrote:I'd be surprised if a bog standard rack didn't work - I've fitted loads, together with mudguards, to this electric bike in my shop - it has fat tyres

The bike's specification does not state the tyre width, only that they are 27.5" Big Bens. The maximum width Schwalbe list for 27.5" Big Ben tyres is only 50mm.

DaveE128
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Re: Pannier racks for 27.5+ boost spacing MTB

Postby DaveE128 » 3 Jun 2019, 8:11pm

Thanks Slowster, that's a very good point! I'll have to have a look at the racks I have and the Tubus drawings.

slowster
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Re: Pannier racks for 27.5+ boost spacing MTB

Postby slowster » 3 Jun 2019, 9:09pm

DaveE128 wrote:Thanks Slowster, that's a very good point! I'll have to have a look at the racks I have and the Tubus drawings.

I cannot help wondering about your proposed choice of bike. I appreciate that 3" tyres will provide more cushioning for your wrists than your gravel bike, but are they (possibly with suspension as well?) the optimum solution? I suspect that an important factor with your gravel bike's effect on your wrists is that you probably have a significant amount of weight on your hands, especially with drop bars and/or a long forward reach.

Since the forward reach of MTBs can vary, it might be that you need to take account of this in any new bike choice as much as the tyre size.

If you need electric assist, then you need it and that's that. However, if it's not essential, then it does add a significant premium to the cost of the bike, and if it was not essential then you might be able to buy something better and possibly more suitable for your particular needs for similar or slightly more money. I say more suitable because there is a much wider range of different types of non-electric assist bike.

I don't know that it would suitable for your needs and it's probably not with your budget, but a bike like the Shand Tam is an example of a bike that is very different from what you are currently considering, and might be even better suited to your needs:

- the high front end and handlebars will reduce the weight and pressure on your wrists
- no electric assist, but the Rohloff provides very low gears
- the Rohloff is probably ideal for off road commuting, given its general reliability, durability and ultra low maintenance
- the Gates belt drive potentially offers similar benefits (although personally I am unconvinced by them, and would either swap to a chain as soon as the first belt wore out or would specify a chain to begin with). Even a chain will still have advantages when used with an internal hub gear compared with derailleur chains
- the Shand has clearance for 29" x 3" tyres, but that would rule out mudguards. However, a 29 x 2.35 or 2.4 tyre might provide all the comfort you need and should allow a rack and mudguards to be fitted.

The Shand is probably a lot more expensive than the ebike you are considering, but it's a bike that is suitable for a lot more than just commuting, and more importantly which will probably still be running as well in 5 years time as when new with only an annual oil change for the Rohloff and the occasional new belt/chain. I suspect an eMTB would cost more to maintain in similar good order and/or would have a shorter useful lifespan of regular hard commuting use.

DaveE128
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Re: Pannier racks for 27.5+ boost spacing MTB

Postby DaveE128 » 4 Jun 2019, 7:02pm

Looks like the Topeak racks have enough clearance (see attachment)

I'm thinking electric because I'm just too tired after riding to work and back. I've been commuting twice a week on a slightly shorter commute for several years and this doesn't seem to be improving :(

The wide tyres seem good for comfort and providing some cushioning to the luggage, and the downsides should be negated by the e-assist.
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slowster
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Re: Pannier racks for 27.5+ boost spacing MTB

Postby slowster » 4 Jun 2019, 7:32pm

It does sound like e assist is the answer for your requirements.

Will you need to spring the base of the rack apart much? I assume it's aluminium and designed for frames with 135mm OLN spacing, compared with the 148mm Boost spacing. I don't know how an aluminium rack would respond to that, or if you could bend it permanently rather than springing it apart.

It certainly looks like there's more than enough clearance for a 3" tyre, and assuming the top of the rack would be high enough above the tyre, it looks like you would have good clearance for a mudguard if you could find one wide enough for 3" tyres.

DaveE128
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Re: Pannier racks for 27.5+ boost spacing MTB

Postby DaveE128 » 5 Jun 2019, 9:33pm

I will need to buy the 29" version of the rack. I suppose one option to reduce/avoid bending might be to cut down the projecting parts at the bottom (intended to provide disc caliper clearance) and use shorter bolts.

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RickH
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Re: Pannier racks for 27.5+ boost spacing MTB

Postby RickH » 8 Jun 2019, 1:24am

DaveE128 wrote:I will need to buy the 29" version of the rack. I suppose one option to reduce/avoid bending might be to cut down the projecting parts at the bottom (intended to provide disc caliper clearance) and use shorter bolts.

You can't cut them down easily as they are receessed holes & use normal length bolts.

You would have to sleeve long bolts & use large washers on the outboard ends if you cut off the bits with the bolt sized hole.

I've found that the topeak rack springs out easily enough - I some times use mine on a Circe Helios tandem which has chunky sliding dropouts bolted inboard a chunky bit of frame so the bolt holes are quite well spaced.

My rack has seen around 9 years of use on the Circe & on 2 other bikes with standard 135 & 130 mm rear hubs. It has not suffered any as far as I can tell.