Guide for setting up skinny tires on lectric xp 2

[towardsdawn]

I had to switch out my tires for skinnier ones to get my bike to fit on my local bike racks (Montgomery County MD RideOn and Washington DC Metrobus). Here's a quick guide for anyone looking to do something similar.

1. Find out the maximum width of tires and weight your bus bike racks will accept. I ended up googling the tech specs for Sportworks which is what my buses use (probably yours too), and the narrowest one is the Sportworks DL2 which has a 55lb weight limit and 2.3in max tire width.

2. Check if your bike meets requirements, including whether or not it will fit in the mounting system. In bike racks with front hook mounting system which goes over the top of the front tire, you'll have to remove the front fender. The Lectric XP 2 with the battery removed and skinnier tires and rims just about clocks in at 55 lb.

3. Decide on a tire width and rim that fits your requirements. At the minimum I would look at rims which are double walled (strong enough for ebikes), 36 holes, with offset rim holes (to accommodate the increased spoke angle from the hub motor) and a tire-rim width combination that is recommended by the manufacturer (I used Schwalbe's tire width and rim width table located here). Good cheap rims would be the SE Bikes J24SG (which I used the 406x24) and the Weinmann DM30. Ideally the rim would also have angled rim holes but I had a hard time finding ones that didn't break the bank.

4. Decide on spoke cross pattern (I used 1-cross, but I think you can get away with radial on the rear hub, which would reduce the spoke angle). Measure for spokes (I posted the measurements of the front and rear hubs here). Input them into a calculator to get correct spoke lengths (I used Freespoke). The lower the flange exit angle, the easier it will be to mount the spokes. I did end up with an exit angle of 31 degrees on the rear hub, which I was just about able to mount on the J24SG rims.

5. Decide on spokes and tires. I would recommend tires certified for ebikes (Schwalbe has ECE-R75 and ebike 50 km/h certification on their tires, Grin recommends 13-14G spokes).

6. Mount your spokes, tires and rims and enjoy! I liked Grin's single-cross wheel build tutorial and Park Tools' wheel truing tutorial

 

[harryS]

Nice job. Single cross is stronger. Did you end putting the spokes on the hubmotor with the elbows all facing out?

 

[towardsdawn]

Nice job. Single cross is stronger. Did you end putting the spokes on the hubmotor with the elbows all facing out?

I did the elbows on the outside of the hub motor, which is what Grin recommends because it makes the wheel more stable

 

[scottsdalecommuter]

love the reflective tape! great idea. I had a mountain bike with wider tires that i had to really jam to get down in the fairly narrow front bus bike rack holder. that's a really nice looking city commuter bike!

 

[m@Robertson]

You can go Waaaaay past the recommended widths on the various manufacturer recommendations. One of the keys to getting it done safely is to oversize the tube. Its common knowledge you can put a Maxxis Hookworm on an 80mm fat bike rim. Thats a 26x2.50 tire. Its often done to lower a bike so a shorter rider can fit onto a one-size-fits-most DTC ebike frame. On similar 80mm rims, I put Schwalbe 26x2.35 Crazy Bobs on and they fit just fine. I used a 3.50 tube - its always a good idea to use an oversized tube on general principles, but on a zany rim combo, it assures the tire fits easily to the rim crochets.

Speaking of combos, look up the DT Swiss Tire Pressure And Dimension table. Thats the best of the manufacturer charts - WTB has another one on a web page. So long as you remember lawyers had to sign off on them, and the true range is a bit more than admitted to, these charts are good references, although again the DT Swiss with its tire widths going up to 5" is the best.

1-cross or radial should only be done as a last resort. You only do that when forced. 2-cross or even 3-cross is what you see on quality wheel builds where the builder is not forced to make compromises. For my own 20" wheel builds a pro wheel builder did 2-cross. One of them was elbows all-outside but that was more because it was so difficult to lace the thing in the first place (used Sapim Leader spokes which was fine from a structural standpoint, but would have been much smarter to use the butted 13/14 Sapim Strongs. Part of a wheel's necessary performance is it should flex, which means using thinner spokes that are high quality so they can flex and spring back without damage. The downside of that is you're spending over $1 per spoke and a bit more on top for a proper length brass nipple. My 26" fat hub wheels are 3-cross. Just barely able to make that happen and not have bad angles.

Speaking of angles, buying rims with angled spoke holes is a HUGE help to stringing the thing with a better pattern. This is my 20" Alienation Blacksheep rim, a BMX rim I use on the front of my Bullitt.

If you have a double-walled rim with straight holes you probably really are stuck with a sucky spoke pattern.

And be judicious about offset-from-center spokes. Part of a bicycle wheel's strength is derived from the triangle the spokes form from the hub to the rim. A quadrilateral is not as strong of a shape as a triangle in this regard. I've done it myself but its when I don't have a choice, not by preference. My 90mm carbon fiber deep dish wheels are not offset one bit and thats a good thing.

 

[jobtraklite]

I've noticed this is the second EBR thread that said only one width sized tire can be used with fat tire wheels. In this case Mr. Towardsdawn replaced both the rim and tire, rather than just the tire. This seems strange to me because I know that non-fat wheels can safely accommodate several different width tires. In fact the late, great Sheldon Brown, the guru in all things bike parts and mechanics, published a chart showing which tire widths safely fit on which interior rim widths.

I don't know the interior width of a fat rim; but I suspect it is greater than 25mm. I guess fat tire bikes didn't exist during Mr. Brown's lifetime. Nevertheless, for example, a tire anywhere between 44mm and 57mm should be OK on a rim with an interior width of 25mm.

I'm interested in the subject because I might like a skinnier tire on my bike. But I'm wondering how narrower I can go from 2.4".

 

[m@Robertson]

I don't know the interior width of a fat rim; but I suspect it is greater than 25mm. I guess fat tire bikes didn't exist during Mr. Brown's lifetime. Nevertheless, for example, a tire anywhere between 44mm and 57mm should be OK on a rim with an interior width of 25mm.

I'm interested in the subject because I might like a skinnier tire on my bike. But I'm wondering how narrower I can go from 2.4".

The DT Swiss tire width chart I llinked above shows what the Sheldon Brown chart does, plus it goes up to fat bike widths. Its a much better chart to use as an example. WTB also has one that is a little more conservative.

 

[jobtraklite]

The DT Swiss tire width chart I llinked above shows what the Sheldon Brown chart does, plus it goes up to fat bike widths. Its a much better chart to use as an example. WTB also has one that is a little more conservative.

The chart you posted has the indexes reversed, so I'm not exactly sure how to use it. However, if I knew the rim inner width, I could read off the recommended tire width. Now if the bike manufacturer used the same chart, then the rim inner width would have to fall within 26 and 30 mm. If the rim inner width were 26 or 27, the recommended tire with would be between 1.7" and 2.4". If it were between 28 and 30, recommended tire width would be between 2.1" and 2.7". Am I reading it right?

While I'm at it, I have a question about the max tire pressure portion of the table. It looks like the max
in the whole table is 73 psi. But I can remember trying to get 23" tires to 100psi.

 

[m@Robertson]

You use the DT Swiss chart just like you would the Sheldon Brown one. The axes are not reversed but they are swapped.

You pick your rim inner width, which is easy to learn via typical rim specs, or take a measurement off a pair of calipers. DT shows you an illustration (measurement B) of what you measure on your rim. That sets your X axis. Your Y axis is then the width of your chosen tire. Where the two intersect is either a white box (bad choice), light grey box (a livable choice) or a dark grey box (sweet spot choice).

The Sheldon Brown chart is a go/no-go and doesn't have the 'possible' range, so the Sheldon Brown chart is much less of a real-world tool. Additionally note the DT doc has an entirely separate chart for hookless rims (typically those are carbon fiber). You have to remember that lawyers signed off on the DT chart, which means your ranges really are a little wider than the chart says they are. So as you cain a bit of experience, you have a very good idea of what is workable for reals.

On max tire pressure, lawyers are doing the talking there. Use the tire pressure limit on the sidewall of your tire and pump to that. Ignore the DT chart. Bike tires generally need to be pumped up to full pressure. The consequences of underinflation can be disastrous to your wheel. Also remember that inflation pressures are cold pressure. The tire pressure will increase significantly as the tire heats up in use (exactly like a car tire does) and this is both expected and not a problem.

Plus parts of that are just plain wrong. I have hookless 90mm carbon fiber rims that have 26x5.05" Snowshoe XL rims. DT Swiss says I can go to 29 psi with a tube and 22 without. That is insanely wrong. 29 psi on a tire that size is going to create a solid rock of a tire that has so much surface area - and so much physical pressure - that I would not be surprised at all if it blew off the rim. In fact, the rim manufacturer says max psi is 15 and even that is a solid rock and too much. A tire that big is actually pretty firm at only 3 psi to give an idea of how far off that chart is.

So... use your charts to give yourself an idea of whats what, but don't rely 100% on ANY chart. You've got to use your brain and your experience to go further than the lawyers - and the dummies - will allow.